The present invention relates to a magnetic recording medium, and particularly relates to a magnetic recording medium having a surface structure effective in preventing stiction between a magnetic head and the magnetic recording medium.
Magnetic recording media such as hard disks have been conspicuously improved in areal density by improved techniques such as finer granulation of magnetic particles for forming magnetic recording layers, alteration of materials, and finer head processing. Further improvement in areal density will be expected in the future. However, the improved techniques adopted till now have elicited problems as to side fringes, crosstalk, etc. due to a limit of head processing and a spread of a magnetic field. Thus, the improvement in areal density using the background-art techniques has reached its limit.
As one of solutions against the problems, that is, as one of techniques, which can improve the areal density of magnetic recording media, there have been proposed discrete track type magnetic recording media (for example, see JP-B-5-22291/(1993) or JP-A-9-97419/(1997)). A typical discrete track type magnetic recording medium has a magnetic recording layer formed with concentric track patterns, and a non-magnetic layer filled into concave portions between adjacent ones of tracks so as to extend continuously in the track direction and separate the concentric track patterns from each other.
For example, Patent Document JP-B-5-22291 discloses a mode of such a discrete track type magnetic recording medium in which a non-magnetic layer provided for separating concentric track patterns from each other is formed as a flat surface in a position higher than the thickness-direction upper surface position on a magnetic recording layer comprised of the concentric track patterns. In addition, Patent Document JP-B-5-22291 discloses another mode in which the non-magnetic layer is formed also on the magnetic recording layer. Also in that mode, as disclosed in Patent Document JP-B-5-22291, the non-magnetic layer provided for separating the concentric track patterns from each other is formed as a flat surface in a position higher than the thickness-direction upper surface position on the non-magnetic layer provided on the magnetic recording layer. Further, Patent Document JP-B-5-22291 discloses the mode in which the non-magnetic layer is formed also on the magnetic recording layer, in which the non-magnetic layer provided as a flat surface for separating the concentric track patterns has the same thickness-direction height as the non-magnetic layer formed as a flat surface on the magnetic recording layer comprised of the concentric track patterns.
In manufacturing of such a discrete track type magnetic recording medium, a non-magnetic material is often filled into a concave portion between adjacent tracks formed by concentric track patterns. Thus, the upper surface of the magnetic recording medium is made flat enough to suppress fluctuation in flying of a magnetic head flying on the magnetic recording medium due to an air flow. As a method for filling the non-magnetic material into the concave portion between adjacent tracks, a film formation technique such as sputtering to be used in the field of semiconductor manufacturing is used. However, when the film formation technique is used, the non-magnetic material is formed not only between the tracks but also on the upper surface of the magnetic recording layer. Thus, a large difference in level is formed on the surface of the magnetic recording medium due to the non-magnetic material formed as a layer on the magnetic recording layer.
Due to the existence of such a large difference in level, the gap length between the magnetic head flying on the magnetic recording medium due to an air flow and the magnetic recording layer is increased. Thus, there occurs a problem that the sensitivity is lowered, the flying height of the magnetic head on the magnetic recording medium is made unstable, or foreign matters are accumulated easily. It is therefore desired to flatten the surface of the magnetic recording layer while removing the non-magnetic material formed as a layer on the magnetic recording layer. A processing technique such as CMP (Chemical Mechanical Polishing), for example, used in the field of semiconductor manufacturing is used as such a flattening method.
However, in any one of the magnetic recording media disclosed in Patent Document JP-B-5-22291, the upper surface of the non-magnetic layer formed out of a non-magnetic material is a flat surface. Thus, there is a problem that a magnetic head flying on the magnetic recording medium due to an air flow in a hard disk drive or the like is stuck onto the flat surface easily, so that the magnetic head is crushed easily. On the other hand, when the aforementioned CMP method or the like is used to flatten the surface of the magnetic recording medium, there is a problem that the magnetic head is easily stuck onto the magnetic recording medium so that the magnetic head is crushed easily.
Further, with a request to increase the areal density, the flying height of the magnetic head may be not higher than 10 nm. In such a case, the magnetic head and the magnetic recording medium are brought into intermittent contact with each other, that is, they have contact with each other on one occasion, but have no contact with each other on another occasion. In this state, when the surface of the magnetic recording medium is too flat, there is a problem that friction between the magnetic head and the magnetic recording medium increases so that the magnetic head is crushed easily for the same reason as mentioned above.